Processes have been known for the preparation of an organo-substituted sodium aluminum hydride (hereinafter abbreviated as SAH) by using sodium, aluminum, organic compounds (1) to (6) described below, and hydrogen as raw materials.
According to the literature, e.g. Japanese Patent Publication No.45-41214(1970) and 47-1452(1972), Inorganic synthesis, Vol. XVIII, 149, and Collection CZ-ECHOSLOV Chem. Commun. Vol. 37, (1972) 1178, there are many processes for preparing SAH represented by the formula: EQU NaAlHxZ.sub.4-x
wherein X is an integer of 1 to 3, and Z is an organic group obtained by eliminating an active hydrogen atom from an organic compound selected from the group consisting of:
(1) an alcohol or a phenol,
(2) a tetrahydrofurfuryl alcohol,
(3) an ether alcohol obtained by alkylating one hydroxyl group of of a diol,
(4) a polyether alcohol obtained by condensation of an ether alcohol and diol so as to remove one mole of water,
(5) a tetrahydropyranyl alcohol, and
(6) a compound having the formula: EQU (R).sub.2 =N(--CH.sub.2).sub.n OH
wherein R is the same or different and is selected from the group consisting of an alkyl group having from 1 to 4 carbon atoms, an alkoxy alkyl group and an aryl group having from 6 to 8 carbon atoms and n is an integer of 2 to 4.
Representative preparation processes are described below. EQU (1) Na+Al+2ZH.fwdarw.NaAlZ.sub.2 H.sub.2 ( 1) EQU (2) NaZ+Al+ZH+0.5 H.sub.2 .fwdarw.NaAlZ.sub.2 H.sub.2 ( 2) EQU (3) 2AlZ.sub.3 +3Na+Al+3H.sub.2 .fwdarw.2NaAlZ.sub.2 H.sub.2( 3) EQU (4) 3NaZ+AlZ.sub.3 +2Al+3H.sub.2 .fwdarw.3NaalZ.sub.2 H.sub.2( 4) EQU (5) NaAlZ.sub.4 +Na+Al+H.sub.2 .fwdarw.2NaAlZ.sub.2 H.sub.2( 5) EQU (6) NaAlZ.sub.4 +NaAlH.sub.4 .fwdarw.2NaAlZ.sub.2 H.sub.2 ( 6) EQU (7) NaAlH.sub.4 +2ZH.fwdarw.NaAlZ.sub.2 H.sub.2 +H.sub.2 ( 7)
Among the above processes, processes(6) and (7) can be readily carried out. However, NaAlH.sub.4 which is expensive and difficult to obtain is used as a starting material and its use leads to high production costs.
Inexpensive raw materials can be used in process (1) which prepares the desired product directly from its constitutional elements and the process favorably gives the product with less steps. However, it is required to continuously monitor and regulate heat generation and variation of hydrogen pressure.
In processes (2) to (5) a part of the sodium and the aluminum is reacted with the organic compounds of the above(l) to (6) (hereinafter abbreviated as ZH) to give complexes. The resulting complexes, e.g. NaZ, Al Z.sub.3 and NaAl Z.sub.4, are further provided with sodium, aluminum and hydrogen to cause hydrogen addition and ligand exchange reaction. The required steps are increased in these processes. However, these processes are nevertheless preferred in view of being able to control heat generation and hydrogen pressure with ease.
As mentioned above, the preparation of SAH is a very complex reaction which simultaneously or individually progresses via a complex forming reaction, a hydrogen addition reaction, a ligand exchange reaction, a ligand removal reaction, a parallel reaction and a polymerizing reaction.
The preparation of SAH includes a hydrogen absorption reaction and thus is generally carried out in a hydrogen atmosphere under high pressure. However, there has been a problem when usual aluminum, i.e., aluminum in a conventional form, is used, the synthesis reaction of SAH cannot proceed unless very high pressure of hydrogen is applied.
When aluminum in its conventional form is used as a raw material, a hydrogen partial pressure of 150 kg/cm.sup.2 or more has been required to perform the industrial production. Such high pressure directly leads to a large increase in the cost of production equipment and is also unfavorable from the standpoint of safety of operation.
When the partial pressure of hydrogen is reduced in carrying out the reaction by neglecting the extension of reaction time, gradually formed SAH decomposes by thermolysis successively and the decomposition leads to a remarkable decrease in the yield and quality of the product.